Testing reagent

ABSTRACT

A reagent composition particularly adapted for use in treating organic samples suspected of containing chemically-bound heavy metals preparatory to electrically detecting and measuring the heavy metal content of the samples. The composition includes an electrolyte vehicle which is essentially free of the heavy metal being detected and measured, a measured quantity of at least one metal ion-containing reagent dissolved therein, said metal ion (1) being adapted to displace the heavy metal from its organic chemical bonding and (2) remaining in electrolytic solution at the electrolytic deposition potentials of the heavy metals being detected and measured, a dispersing agent, and a hydrogen ion source for adjusting the pH of said composition to pH about 1.

RELATED APPLICATIONS

This application is a divisional of co-pending application Ser. No.666,664, filed Mar. 15, 1976, which in turn is a continuation ofapplication Ser. No. 505,149, filed Sept. 11, 1974 (now abandoned),which in turn is a division of application Ser. No. 447,376, filed Mar.1, 1974, which was abandoned in favor of application Ser. No. 643,295,filed Dec. 22, 1975 (now abandoned) of Wayne R. Matson.

BACKGROUND OF THE INVENTION

It has long been possible to test both qualitatively and quantitativelyfor ionic materials in an aqueous sample by electrolytic means, and torecord the electric potential of deposition of the ions on an electrode.In one form of such testing known as stripping voltammetry, the ions arefirst deposited on an electrode and thereafter the potential iscontinuously or continually varied to strip the deposited material fromthe electrode and redissolve it in the sample liquid. This operation isknown as stripping voltammetry and since it is ordinarily used byplating cathodically and stripping anodically to detect and measuremetallic ions, it is often known as anodic stripping voltammetry. Bymeans of anodic stripping voltammetry, it has been found possible toperform relatively quick simple and accurate tests to measure minutetraces of appropriate materials. Recently, in connection withenvironmental studies, it has become important to collect smallquantities of polluting impurities from the atmosphere or from otherportions of the environment to test for the presence of dangerouspollutants. A very immediate concern has been the need to test for thepresence of informative or dangerous impurities in the humanbloodstream, and anodic stripping voltammetry has proven itself capableof performing such tests. The present inventor and his associates havebeen interested in problems relating to this general field of activityfor a number of years. Among other things, they have devised anddeveloped certain useful apparatus for anodic stripping voltammetry asdisclosed in application Ser. No. 167,330 and certain improvedelectrodes disclosed in Ser. No. 168,161 and Ser. No. 327,788. Thepresent invention is a unified system for anodic stripping voltammetryor cathodic stripping voltammetry capable of performing analysis oftrace materials on an extremely rapid and an extremely accurate basis.In particular, the system according to the present invention can analyzehuman blood samples in the field or in the normal environment of suchhuman beings at the rate of many hundreds of samples per day and canobtain critical output data regarding the presence of impurities such aslead, cadmium, zinc or the like in the human bloodstream within about aminute after a blood sample is actually taken from the human being, thuspermitting such sampling in the environment of the real world. Thequickness of completion of testing is of unusual importance, in light ofexperience which shows that the 7% of people tested in urban slum areascannot later be located if they are once allowed to leave the test area.

GENERAL NATURE OF THE INVENTION

The present invention is a unified system, preferably automated, forelectrochemical testing. In its usual embodiment it is an automatedsystem for anodic stripping voltammetry. According to a preferred formof the invention, a sample holder is removably positioned to receive aspecial electrode having a very large, smooth active electrode surface.On the turn of a switch, electrical means are actuated to apply acathodic potential to the electrode, plating out cations on theelectrode, after which the electrical means apply the operating anodicvoltage to strip out the deposited cations and monitor the potential andcurrent.

The anodic stripping potential desirably is pulsed and the pulsedchanged in voltage in a stepwise mode. Each step desirably is raised0.01 volts. The initial few pules on each step are ignored and theremainder are counted and measured. The readout is either charted ordigitalized. The potential at which electrolytic current flows is anidentification of the specific cations being stripped, and the quantityof current is a quantitative measure of the cation.

A presently preferred use and application of the invention ismeasurement of heavy metals such as lead in the human blood stream. Ablood sample is taken, and an aqueous solution containing a metallic ionsuch as Cr³⁺ or Ca²⁺ is added to exchange with the lead complexed withthe blood. The sample is then placed in operating position on theapparatus and the switch turned on. A lead content of 40 micrograms oflead per 100 ml of blood is a recognized standard of a dangerous levelof lead in the human blood stream. In broader usage and application,identification and measurement of different metals in blood is nowthought to have medical diagnostic value: for example, the profile ofzinc and copper appear to be one diagnostic test for leukemia.

The apparatus according to the present invention can employ variouskinds of waveforms to accomplish various different tests and toaccommodate numerous electrical or chemical problems. The output may bein chart form, but one of the advantageous results is that there can bedirect digital readout obtained essentially automatic and directlycalibrated in end units; in practice, for example, the digital readoutof lead in blood samples is directly in terms of micrograms of lead per100 ml of blood. With calibrated digital readout, all the operator needdo is record a single number.

The cell and electrode structure employs a hollow electrode with innerand/or outer surfaces active. Coaxial stirring produces reliable,reproducible results with an unusually fast time constant, and thepreferred chemical ion exchange procedure joins with structure andmethod to give results on the spot. As presently in practical use, thesystem gives test results on biological samples within a minute or two,and it is well adapted to give equally fast results on other types ofsamples.

The system also has a high degree of flexibility to use conventionallyprepared (digested) samples or non-digested samples, to use biologicalmaterial such as blood or tissue or non biological samples such aspaint, gasoline or other "environmental" materials for tests of lead orother metals, to use industrial materials for sampling and testing, andto test for a wide variety of metals including lead, cadmium, copper,zinc, thallium, silver, gold, bismuth and the like.

The nature of the invention is further illustrated in the drawing inwhich:

FIG. 1 is a perspective view of testing apparatus according to oneembodiment of the invention.

FIG. 2 is a front view, partially in section, of sample supportapparatus according to the embodiment of FIG. 1.

FIG. 3 is a front view, partially in section of electrode assemblycomponents according to another embodiment of the invention.

FIG. 4 is a block diagram of an electrical system in conjunction withapparatus according to one embodiment of the invention.

FIG. 5 is a front view of a front control panel of apparatus accordingto a modified embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 is illustrated a cabinet generally designated 10 on which ismounted a support assembly 11 serving as a cell and motor support.Mounted on the support assembly 11 is a motor 12. Mounted beneath thesupport assembly 11 is an electrode 13 held in an electrode head 14. Theelectrode 13 is adapted to fit within a sample holder (not shown). Thesample holder in practice is a plastic or glass member shape essentiallylike a test tube and characterized by being made of a material which isfree from detectable quantities of any metal for which testing is to beperformed. One principal intended use of the apparatus, according tothis invention, is testing for trace quantities of lead and accordingly,the sample holder is made of lead-free glass or plastic which has beenadditionally treated to eliminate detectable trace quantities of lead.Desirably the support assembly 11 is pivotally mounted in the cabinet bymeans of mounting pins 16 whereby the entire assembly may be rotated inour out of position for easy insertion or removal of a sample holderfrom the head 14 on which it is held by a snug fit between the head andthe sample holder.

On the cabinet is positioned in a convenient location, an off/on switch17, an off/on motor switch 18, and desirably, a reset switch 19. Also,on the front of the cabinet is a meter 20 for visual read out of voltageor current a recorder off/on switch 21, a sweep offset 22, and arecorder offset button 23. Desirably, there is also on the cabinet facea current range indicator 24.

In FIG. 2 is illustrated further detail of the cell and motor assembly.Mounted on support assembly 11 is motor 12 having a shaft 26 extendingtherefrom. By means of a coupling 27 the shaft 26 is connected to apropeller shaft 28 which terminates in a propeller blade 29 positionedwithin and near the bottom of electrode shield 14. Mounted at the bottomof support assembly 11 is an electrode holder 31 which is adapted andpositioned to hold the electrode shield 14. Mounted within the electrodeshield 14 is a stop 32 receiving and bearing against the electrodeshield 14. The electrode 33 is in turn positioned within the stop 32 andis held in its proper position thereby. Mounted within the electrode aredividers 35 forming internal electrode compartments through whichextends propeller shaft 28 and which, among other thing, serves as aguide for the propeller shaft. In practice three dividers are employedto form compartments. A bearing 36 at the bottom of the electrodecompartment rotatably holds and guides the propeller. Optionally, a finetube 37 or nitrogen line is positioned extending through the electrodeshield and electrode with its nozzle positioned within the electrodecompartment to assure a neutral atmosphere.

The electrode 33 is constructed and adapted for anodic strippingvoltammetry or other electrode chemical operation. The electrode 33consists of a hollow cyllindrical electrode 40 desirably having one ormore openings 41 in its side. The electrode body 40 according to oneform of this invention is a hollow cylinder of graphite impregnated witha film forming material such as paraffin wax or the like and having onits surface a deposit of an electrode surface layer such as, forexample, a layer of mercury. The electrode surface layer is present inthe form of a multiplicity of dots or islands of mercury, eachdepositied on a graphite point and surrounded by a portion ofimpregnated wax surface. The electrode can be produced by impregnating agraphite rod with wax, scraping the wax from the graphite surface to laybare a multiplicity of graphite points and coating mercury thereon byelectrode chemical disposition using the graphite body as an electrodechemical cathode. The preparation of mercury coated graphite electrodedescribed in co-pending application Ser. No. 168,161 referred to hereinbefore.

In at least exposed active areas of the electrode area 33 according toone embodiment of the invention, both the outer surface 42 and the innersurface 43 of the electrode body 40 are coated with the electrode metalas described. When the apparatus of the present invention is employedfor testing for trace elements of lead, the electrode metal preferablyis mercury. In this manner a mercury electrode surface is positionedvertically within the saample holder and has an extremely high ratio ofsurface area in relation to sample volume. The area/volume relationshipshould be at least 3 cm² electrode area per milliliter sample volume,and preferably 4:1 or greater. At present, an electrode to sample ratiois 20 cm² per 3.6 milliliter sample. The propeller shaft 28 passesthrough the center of the electrode 33 and propeller blade 29 ispositioned near the base of the electrode and is adapted to causecirculation of the sample liquid both inside and outside the electrodebody 40.

Apparatus of the type herein disclosed can be employed by means ofmanual switching and manual controls in anodic stripping voltammetry. Insuch manual operation a sample holder containing a liquid for test isplaced in position with the electrode assembly immersed therein. Theelectrode is connected in cathode mode to a suitable power source andionic components are deposited on the electrode surface. In particular,if the apparatus is employed to test for the presence of lead, then leadis electrolytically deposited on the mercury electrode surface and isalloyed therein. After cathodic deposition on the electrode surface, theelectrode is placed in anodic mode and the voltage applied thereto isgradually raised, and the electrolytic current is monitored. Metallicelements are identified by the potential or voltage of which the flow ofcurrent indicates that a trace of metal is being anodically strippedfrom the electrode and the quantity of the trace element is measured bythe quantity of anodic current.

In FIG. 3 is illustrated a modified electrode assembly in which theelectrode 13 is mounted on a support or holder 31 and adapted to fitwithin a suitable sample holder (not shown) in much same manner as withthe assembly in FIG. 2. A coupling 27 connects the motor 12 (see FIG. 1)with a propeller shaft 28 extending axially through holder 31 and to apoint approximately level with the electrode 13. The electrode 13 ishollow, as with the electrode shown in FIG. 2, and within the hollowelectrode the propeller shaft 28 is of significantly bigger radiusleaving only a relatively small space between shaft 28 and inner surfaceof electrode 13. At the bottom of this shaft, once again, is a propellerblade 29. A counter electrode 30 extends through the electrode holder 31and is positioned to be immersed in the sample within the sample holder.A reference electrode 34 also extends through the holder 31 to aposition within the sample. Desirably, the counter electrode 30 is aplatinum wire which may directly contact the solution or, as presentlypreferred, is a platinum electrode contained in a porus glasscompartment or shell. The reference electrode desirably is a silver orsilver cloride wire immersed in a saturated sodium chloride solution.Desirably the propeller shaft 28 may extend through one or severalbearings 21. In the preferred form of the structure, the electrodeholder 31 is adapted to fit snuggly with in a sample holder so thatduring operation a sample holder is retained firmly but releasably in aposition into which it can be manually fitted.

In one form of the invention, as illustrated in FIG. 3, the electrode 13has a coating 15 on its outer or exposed surface. This coating is aplastic tubing shrunk around the outside of the active electrode. Whenthe coating is employed, the electrode is generally protected fromaccidential damage and can, in fact, be handled carefully when theelectrode is removed from a sample. There is relatively small clearancebetween the electrode and the sample holder when in position, and againis there relatively small clearance between the electrode and the lowerend of stirrer 28. Moreover, the stirrer 28 is slightly tapered, beingslighty larger at its lower end than it is at the upper end, so that thespace between this stirrer 28 and the inner electrode surface also istapered, being narrower at the bottom than at the top. As the stirrerrotates within the electrode, this tapering causes not only localizedcurrents of the test liquid, but also causes a general flow of theliquid downwards in the space between stirrer and electrode.

In high speed sample testing it is important that the sample liquidshould circulate well, but it is also desired that the relatively stilllayer adjacent to the electrode be as thin as practical. This layer,known as the Nernst layer, appears to be about 1-2 micron in theapparatus of FIG. 3.

In FIG. 4 is illustrated, in the form a block diagram, the electricalcontrols for automation of the equipment according to one embodiment ofthe invention. A clock generator and timer controlled sequence serves asa control mechanism for all functions. A plate and strip control 51serves to apply a plating potential to the electrode and under thecontrol of the timer 50 applies such control for a perios of one minuteor selectively for some other period of time such as 3 minutes or 5minutes. A motor 52 energizes the stirring mechanism (propeller shaft 28and 29) and under the control of timer 50, causes stirring of the samplewhile the plating potential is applied.

A sweep generator 53 is adapted to supply a stripping voltage toelectrode 32 and under the control of timer 50, supplies this voltage 10seconds after the plate and strip control 51 and motor 52 and turned offby the timer 50. The sweep generator 53 is essentially a staircasegenerator and steps down in 10 millivolt steps at 100 milliseconds perstep. When the apparatus is used for detection and measurement of lead,the plating voltage is -1.0 volts and the sweep generator steps downfrom -1.0 volts to 0.1 volts in 90 steps in an elapsed time of aboutnine seconds. The sweep generator operates through an electrode supply54.

Adapted to read out from the electrode during stripping, and optionallyduring plating, is an I/E converter which serves to convert current tovoltage to supply a signal more suitable for being amplified. The I/Econverter 55 feeds to an optional strip chart recorder 56. As will beseen hereinafter, the apparatus under the control of the elements inFIG. 4 produces a direct digital readout but a chart readout may bedesired and is illustrated in FIG. 4. This readout, when employed, is aconventional charting device to chart current flow vs. time; the currentflow being expressed in terms of voltage output from the I/E converter55. The time vector, is relation to the output of sweep generator 53,identified and stripping voltage. The chart represents, therefore, thereadout from the electrode and is shown in the figure as an analogselector 57.

As S & H I/E zeroing unit 59 (sample and hold) delays for a selectedtime which, in operation, may be 20 milliseconds, before counting theelectrode output. In order to eliminate initial noise upon each changein step as the stripping potential is stepped down, an I/E zero selector60 is set for a zero point at 100±50 millivots before the integrationzone.

A connection to a power supply or voltage source 61 operates throughswitch 62 energize the various electrical components, energizes thetimer 50 and the other power units previously and hereinafter described.For digital readout, which is a presently preferred embodiment of theinvention, a dual slope integrator 64 integrates the output signal andconverts the analog signal to a digital representation. An S & Hintegrator 65 operates from the dual slope integrator 64 to identify andisolate the zone of the stripping potential in which the current signaloccurs. An S & H delayed analog 66 optionally permits a variation insample and hold time. This adjustability is not required if theapparatus is employed for a single use and the application, as is nowthe case where the apparatus is employed for the detection of lead whichhas a single deplating or stripping potential.

An integration set point and logic circuit 68 is adapted to receive thereadout signal and to discard as noise an initial signal less than apre-determined value. This integration setpoint and logic 68 then,together with an output from the dual slope integrator 64, feeds to anup/down count control logic 69. This up/down count control logic 69, forits first count, counts down six times and next, for twelve counts,counts up followed by a fourteenth count which, once again, counts downsix times thus making a count equivalent to a digital output from theoutput signal. The up/down count control logic 69 in turn feeds to anup/down counter 70 and to a data latch 71 which finally feeds to adigital readout 72. The up/down counter 70 merely counts the signalreceived from the up/down counter control logic 69 in the number anddirection designated by such logic. The data latch 71 brings the processto a halt after the signal in the desired zone has been completed. Thedigital signal received from the total count from up/down counter 70 andis converted into a digital reading thus corresponding to a digitalrepresentation of quantity of metal or other ion detection andmeasurement. In practice, this readout is set to present digitally adirect reading of micrograms of lead per 100 cc of blood sample. Thedigital readout 72 can, accordingly, be set to translate a signal tocorrespond to any desired digital measure.

In FIG. 5 is shown the panel of apparatus which may operate inaccordance with the diagram of FIG. 4. The upper part of the panel isnormally visible; the lower portion may be covered after the appropriatesettings and calibration are made.

A digital display 80 reads out and displays the digital record of a testwhile a meter 81 may indicate the current flow or voltage during a run.An indicator lamp panel has lights for "ready" 83, "plate" 84 and"strip" 85 indicating the phase of the operation. A push button 86labelled "cancel analysis" operates to interupt and return the analysisto zero. At the upper right hand corner a push button 87 labelled "startanalysis" is adopted to start timer 50, and pushing this button is theonly act required of the operator once the sample is in place. A motorlight 88 indicates when motor 52 is operating.

Adapted for preliminary set up and calibration is a lower panel. Apotentometer 90 is adjustable, being adapted to control the digitalreadout 72 of FIG. 4, desirably so that the readout is directly in thecorrect digital units. When blood is tested for lead, this readout isset against a known standard sample so that the readout is the number ofmicrograms of lead per 100 milliliters of blood. A rotary switch 91selects a desired scale expansion if needed, and a blank correctionpotentiometer 92 is adjustable to set a desired zero point.

In the lower left corner of the panel is a run indicator 93, with screwpotentometers 94, 95, 96, 97 and 98 for indicated settings for initialpotential, sweep rate, recorder set point and recorder integration.Finally, in the lower right is a slope correction setting 99, a rotaryswitch 100 selecting one of several automatic time controls for timer 50(or selecting a manual control) and a "function test" switch 101 forselecting a dummy cell or analysis cell for calibration or otherpurposes.

The panel of FIG. 5 serves the purpose that in part illustrates theinstrument and in part illustrates the ease of operation. A skilledoperator can first set and calibrate the instrument for a specific testcondition, after which an operator who may be unskilled measures apredetermined quantity of sample into a prepackaged sample holder,places the sample holder on the machine, pushes the "start analysis"button 87 and a minute later reads the result in digital display 80.

The apparatus discussed, herein in accordance with the present inventionis intended to be employed for detection and measurement of tracequantities of certain heavy metals including zinc, cadmium, lead,copper, bismuth, silver, gold and thallium. Analysis can be made ofnanogram quantities of these trace metals in periods of time of a fewseconds up to one or occasionally several minutes. In particular, it ispossible to detect and measure quantities of certain of these traceelements in the human blood stream. One of the very important socialpurpose of this invention is the detection and measurement of smallquantities of lead in the human blood stream and in particular, in theblood stream of children residing in city slum areas.

For such lead detection and measurement, the desired sample holder is atest tube shaped plastic or glass vessel made of lead-free glass orlead-free plastic or other convenient container. Desirably, the sampleholder is preconditioned by electro-chemical treatment to electrolyzeout of the glass any trace quantities of lead which may originally havebeen present. A reagent solution is prepared in advance containing adissolved chromium or calcium ionic material Cr⁺³ or Ca⁺². A measuredsample of blood is taken from a human blood stream. A small quantity ofthe chromium or calcium reagent is added, and as presently preferred, amixed calcium-chromium reagent is employed. The precise amounts andconcentrations can be adjusted for convenience, provided a standardprocedure is adopted and suitable calibration made. It has been foundsatisfactory to employ CrCl₃ prepared with 0.03 to 0.04 molar Cr⁺³ in0.001 to 0.02 molar HCl; this chromium ion solution may be employed inthe amount of 3.6 cc to exchange the lead in 100 microliters of bloodsample. In one embodiment there is used a dilute solution of calciumchloride, chromium trichloride, hydrogen ion, perchlorate ion and adispersing agent (Surfynol 104 is the agent currently employed, and isbelieved to be a non-ionic higher alcohol wetting agent). One formulawhich has been used with biological samples such as blood, foods, is:

    ______________________________________                                        CaCl.sub.2         0.08F                                                      CrCl.sub.3         0.04F                                                      HgCl.sub.2         0.000225F                                                  H.sub.2 NNH.sub.2 --(HCl).sub.2 (hydrazine)                                                      0.019F                                                     Surfynol 104       0.001 weight percent                                       ClO.sub.4 -        0.458F                                                     H+                 0.0398 (to bring to pH 1.4)                                ______________________________________                                    

Another formula which is now presently preferred is different in somedetails of composition and is now thought to be more reliable for usewith fresh human blood samples, and comprises:

    ______________________________________                                        Calcium Acetate      0.08F                                                    CrCl.sub.3           0.04F                                                    HgCl.sub.2           0.000225F                                                H.sub.2 NNH.sub.2 --(HCl).sub.2 (hydrazine)                                                        0.019F                                                   Surfynol 104         0.001 weight percent                                     H.sub.3 PO.sub.4     0.01F                                                    H+                   to bring to pH 1.0                                       ______________________________________                                    

The mixture of calcium ion and/or chromium ion cause release ofcomplexed lead in the blood so that the total concentration of lead inblood can be effectively measured when one of the reagents justdescribed is employed in the equipment and method of the invention.

Heavy metals which are complexed or bound in other sample materials canalso be released. For example, a mix of 0.01 molar bromide ion; 0.1molar NaCl; 0.01 molar HNO₃ ; and 0.01% Triton X-100 (a polyalcohol) issuitable for releasing lead in gasoline. The same and other releasingcomponents can be used to release the various neavy metals from a widevariety of organic samples. What is used is a metal ion or mixture ofmetal ions which will displace the test metal and which will not plateout or strip out at the plating or stripping potentials used indetection and measurement of the metal being tested.

After the test material is treated with a release agent, or after othersample preparation as may be necessary such as digestion, or othertreatment and dilution or concentration as needed, the sample in thesample holder is placed in position on the apparatus and the apparatusis turned on. The chromic ion in the solution acts to displace lead fromany complexes which it may have formed with components off the bloodsample, and the chromium does not plate out at the operating potentialsused for lead analysis. Within a sixty second operating time, theapparatus will cause any lead to be largely deposited on or in themercury electrode coating and thereafter anodically stripped from theelectrode with both identification and quantitative measurement. Animportant value of the invention is that the detection and measurementcan be carried out in a time of no more than a minute or two afterextraction of the blood sample from the blood stream so that the personhimself can be advised as to the test results without being required toreturn on a subsequent occasion or even being required to wait for asignificant period of time for such test results.

A presently preferred sample holder is a self-contained unit which isfactory preconditioned. It comprises a plastic sample holder cylindricalin shape having a volume of 5 cc. and containing 3.6 millimeters of aliquid sample which contains chromic ion, mercury, hydrogen andhydrochloric acid. It is sterilized, purified to remove lead, or toremove other metallic ion being tested and measured and sealed.

What is claimed is:
 1. A reagent composition for treating an organicsample suspected of containing chemically-bound heavy metal preparatoryto electrochemically detecting and measuring the heavy metal content ofsaid organic sample, said composition comprising in combination:anelectrolytic vehicle which is essentially free of said heavy metal beingdetected and measured, a measured quantity of at least one metalion-containing reagent dissolved therein, said metal ion (1) beingcapable of displacing said heavy metal from its organic chemical bondingwhile (2) remaining in electrolytic solution at the electrolyticdeposition potentials of the heavy metals being detected and measured, adispersing agent, and a hydrogen ion source for adjusting the pH of saidcomposition to pH about
 1. 2. The composition of claim 1, wherein saidorganic sample comprises a biological sample and the heavy metal beingdetected and measured is lead, and wherein said metal ion-containingreagent comprises chromic ion or calcium ion.
 3. The composition ofclaim 1, wherein said metal ion-containing reagent comprises a mixtureof chromic ion and calcium ion.
 4. The composition of claim 1, whereineach ingredient of said composition in measured quantity is prepackagedand contained within a sealed sample holder which is also essentiallyfree of the heavy metals to be detected and measured.
 5. A compositionfor treating a human blood sample preparatory to electrochemicallydetecting and measuring the lead content of said sample, saidcomposition comprising:an electrolytic solution containing a dissovledchromic compound and a dissolved calcium compound, the chromic andcalcium ions together being present in concentration of about 0.12 F,dissolved mercuric chloride in a concentration of about 0.000225 F,hydrazine in a concentration of about 0.019 F, phosphoris acid in aconcentration of about 0.01 F, a dispersing agent, and a source ofhydrogen ions to bring said composition to pH about
 1. 6. Thecomposition of claim 1, wherein said organic sample comprises abiological sample selected from the group consisting of blood, tissue,and food.
 7. The composition of claim 1, wherein said organic samplecomprises a non-biological sample selected from the group consisting ofpaint and gasoline.
 8. The composition of claim 1, wherein said organicsample is suspected of containing a heavy-metal selected from the groupconsisting of lead, cadmium, copper, zinc, thallium, silver, gold,bismuth and mixtures of two or more of said group, and said metalion-containing reagent comprises chromic ion or calcium ion.
 9. Thecomposition of claim 1, wherein said organic sample is suspected ofcontaining a heavy metal selected from the group consisting of lead,cadmium, copper, zinc, thallium, silver, gold, bismuth and mixtures oftwo or more of said group, and said metal ion-containing reagentcomprises a mixture of chromic ion and calcium ion.
 10. The compositionof claim 1, wherein said dispersing agent comprises a non-ionic alcohol.11. A composition for treating a gasoline sample preparatory toelectrochemically detecting and measuring the lead content of saidsample, said composition comprising:an electrolytic solution containingdissolved sodium ion in concentration of about 0.1 molar, dissolvedbromide ion in concentration of about 0.01 molar, a dispersing agent,and a hydrogen ion source for adjusting the pH of said composition to pHabout
 1. 12. The composition of claim 11, wherein said dispersing agentcomprises a non-ionic alcohol.